For avoiding an accident situation, an elevator car has a safety mechanism that stops the movement of a falling elevator car by gripping hold of a guide rail of the elevator car. Generally the safety mechanism is designed in such a way that it is able to stop only a downward-moving elevator car. The safety mechanism is usually activated by an overspeed governor. The overspeed governor can be disposed in the elevator hoistway or in a machine room. The overspeed governor is connected to the safety mechanism with a rope, which runs around a freely rotating rope pulley of the overspeed governor. The safety mechanism is activated by stopping the movement of the rope pulley/rope when the elevator car is moving downwards. The overspeed governor has an activation means based on centrifugal force, which means activates the safety mechanism by locking the rope pulley into its position when the speed of the elevator car/rope pulley reaches a certain threshold value.
In newer elevators a safety contact, which is in the safety circuit of the elevator, is fitted in connection with the activation means functioning with centrifugal force. The safety contact opens with the control of the activation means, generally slightly before the locking of the rope pulley. Opening of a safety contact causes an emergency stop of the elevator, in which case the machinery brakes engage to brake the traction sheave of the hoisting machine of the elevator and the power supply to the electric motor of the hoisting machine is disconnected. Unlike the aforementioned safety mechanism, the machinery brakes are also able to stop the upward movement of the elevator car.
Installation of a safety contact in the overspeed governor of an old elevator does not usually succeed in a sufficiently reliable manner, in which case upgrading the safety of an old elevator to conform to current requirements is contingent on replacement of both the overspeed governor and possibly also the safety mechanism of the elevator car. This increases the work phases and costs in the modernization of an elevator.
The speed of an elevator car can increase to be very high before the overspeed monitoring of the overspeed governor functions. For example, the speed of an elevator having a rated speed of 1 m/s can accelerate to a value of 1.5 m/s before the speed of the elevator car starts to decelerate. Such a high speed can be a safety risk e.g. to a serviceman who is driving a service drive with the elevator car while on the roof of the elevator car.
Normally in the elevator hoistway are limit switches on both sides of a stopping floor, the purpose of which limit switches is to prevent the elevator car drifting away from the stopping floor when the doors are open. The arrival of the elevator car at a limit switch when the doors are open activates the machinery brakes of the hoisting machine and/or the safety mechanism of the elevator car, in which case the movement of the elevator car stops. After this the elevator is also removed from use for safety reasons.
Before arriving at a limit switch from its last stop, the elevator car has already had time to travel a distance that produces an appreciable step between the floor of the elevator car and the stopping floor. A step is a tripping risk and injury risk to passengers crossing it. In addition, a step hampers the unloading of a load from the elevator car.
The automatic door of an elevator is opened and closed by driving the door panels with an electric motor. The speed of the door panels is adjusted by adjusting the current of the electric motor with a control unit. In an error situation the speed of the door panels can change suddenly, which might feel disturbing to a person walking through the door.